LZMA(1) LZMA utils LZMA(1)
23 Dec 2005
NAME
lzma, unlzma, lzcat - LZMA compression and decompression tool
SYNOPSIS
lzma [-123456789cdefhkLqtvV] [-S suffix] [filenames ...]
unlzma [-cfhkLqtvV] [-S suffix] [filenames ...]
lzcat [-fhLqV] [filenames ...]
DESCRIPTION
LZMA (Lempel-Ziv-Markov chain-Algorithm) is an improved version of
famous LZ77 compression algorithm. It was improved in way of maximum
increasing of compression ratio, keeping high decompression speed and
low memory requirements for decompressing.
lzma command line tool has a similar interface to gzip(1) and bzip2(1)
and is intended to make use of LZMA compression easy for the users who
are already familiar with gzip and bzip2.
In this manual lzma is compared mostly to bzip2 because that is
currently one of the most widely used free software to compress tar
files made for distribution. Comparing lzma to gzip is not practical
because neither lzma nor bzip2 can compete with gzip in compression
speed. On the other hand the compression ratio of gzip is worse than
of lzma and bzip2.
lzma provides notably better compression ratio than bzip2 especially
with files having other than plain text content. The other advantage
of lzma is fast decompression which is many times quicker than bzip2.
The major disadvantage is that achieving the highest compression
ratios requires extensive amount of system resources, both CPU time
and RAM. Also software to handle LZMA compressed files is not
installed by default on most distributions.
When compressing or decompressing with lzma, the new file will have
the same ownership information, permissions and timestamps as the
original file. However the this information is not stored into the
compressed file like gzip does.
STREAMED VS. NON-STREAMED
LZMA files can be either streamed or non-streamed. Non-streamed files
are created only when the size of the file being compressed is known.
In practice this means that the source file must be a regular file. In
other words, if compressing from the standard input or from a named
pipe (fifo) the compressed file will always be streamed.
Both streamed and non-streamed files are compressed identically; the
only differences are found from the beginnings and ends of LZMA
compressed files: Non-streamed files contain the uncompressed size of
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the file in the LZMA file header; streamed files have uncompressed
size marked as unknown. To know where to stop decoding, streamed files
have a special End Of Stream marker at the end of the LZMA file. The
EOS marker makes streamed files five or six bytes bigger than non-
streamed.
So in practice creating non-streamed files has two advantages: 1) the
compressed file is a few bytes smaller and 2) the uncompressed size of
the file can be checked without decompressing the file. To view the
data stored in the LZMA header use lzmainfo(1).
OPTIONS
Short options can be grouped like -cd.
-c --stdout --to-stdout
The output is written to the standard output. The original files
are kept unchanged. When compressing to the standard output there
can be only one input file. This option is implied when input is
read from the standard input or the script is invoked as lzcat.
-d --decompress --uncompress
Force decompression regardless of the invocation name. This the
default when called as unlzma or lzcat.
-f --force
Force compression or decompression even if source file is a
symlink, target exists, or target is a terminal. In contrast to
gzip and bzip2, if input data is not in LZMA format, --force does
not make lzma behave like cat. lzma never prompts if target file
should be overwritten; existing files are skipped or, in case of
--force, overwritten.
-h --help
Show a summary of supported options and quit.
-k --keep
Do not delete the input files after compression or decompression.
-L --license
Show licensing information of lzma.
-q --quiet
Suppress all warnings. You can still check the exit status to
detect if a warning had been shown.
-S --suffix .suf
Use .suf instead of the default .lzma. A null suffix forces
unlzma to decompress all the given files regardless of the
filename suffix.
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-t --test
Check the integrity of the compressed file(s). Without --verbose
no output is produced if no errors are found.
-v --verbose
Show the filename and percentage reduction of each processes
file.
-V --version
Show the version number of lzma.
-z --compress
Force compression regardless of the invocation name.
-1 .. -9
Set the compression ratio. See the next chapter for detailed
information. These options have no effect when decompressing.
--fast
Alias to -1.
--best
Alias to -9.
COMPRESSION OPTIONS AND MEMORY USAGE
The compression options of lzma are divided to two groups. The first
two (-1 and -2) are designed for fast compression speed. -3 .. -9
provide good to excellent compression ratio but require more CPU time
and system memory.
For relatively fast compression with medium compression ratio -1 is
the recommended setting. It's faster than 'bzip2 --fast' and usually
creates smaller files than 'bzip2 --best'. -2 makes somewhat smaller
files but doubles the compression time close to what 'bzip2 --best'
takes.
Generally for excellent compression ratio, acceptable compression time
and memory requirements (about 83 MB for compression, 9 MB for
decompression) you should use -7 which is also the default. -8 and -9
will give some gain especially with bigger files (>=tens of megabytes)
but also increase the CPU and memory requirements dramatically. See
the table below for memory requirements of different compression
settings.
Flag Compress usage Decompress usage
-1 2 MB 1 MB
-2 12 MB 2 MB
-3 12 MB 1 MB
-4 16 MB 2 MB
-5 26 MB 3 MB
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-6 45 MB 5 MB
-7 83 MB 9 MB
-8 159 MB 17 MB
-9 311 MB 33 MB
DIAGNOSTICS
Exit status:
0 - Everything OK.
1 - An error occurred.
2 - Something worth a warning happened but no errors.
AUTHORS
The LZMA algorithm and the implementation used in LZMA utils was
developed by Igor Pavlov. The original code is available in LZMA SDK
which can be found from http://7-zip.org/sdk.html .
lzma command line tool was written by Ville Koskinen.
http://tukaani.org/lzma/
This manual page is inspired by manual pages of gzip and bzip2.
SEE ALSO
lzmadec(1), lzmainfo(1), gzip(1), bzip2(1)
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